Work machine

ABSTRACT

A work machine having: a working part; a holding part for holding the working part; and an operating part for rotating the working part around the holding part; further comprising: an angle sensing means for sensing the angle of the working part from the horizontal; and a controller for adjusting and holding the position of the working part by use of the operation means based on the angle sensing means.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a work machine, such as an agriculturalmachine or a construction machine, having a bucket, booms supporting thebucket, and dump cylinders for rotating the bucket around the booms.

2. Description of the Relate Art

In conventional work machines having a working part such as a bucket, anoperator operates the bucket by use of a bucket control lever. In otherwords, the bucket is operated by the operator manually. Therefore,during operation, it is difficult for the operator to recognize theexact angular position of the bucket. To address this problem, patentpublications, such as WO2002/040783 and U.S. Pat. No. 5,887,365 havedisclosed new methods. These inventions have a control unit thatcontrols automatic bucket operation, and the control unit recognizes theangular position of the bucket. Then, the control unit adjusts thebucket position according to a target slope angle and a target depth ofexcavation.

Problem to be Solved by the Invention

During excavation work, it is sometimes necessary to keep a loadedbucket level. However, it is difficult for an unskilled operator (adriver) to do so. The two above-mentioned patent publications do notpresent the solution for this problem. Therefore, this invention offersa work machine, which is able to keep a loaded bucket level easily.

SUMMARY OF THE INVENTION Means to Solve the Problem

A work machine having: a working part; a holding part for holding theworking part; and an operating part for rotating the working part aroundthe holding part; further comprising: an angle sensing means for sensingthe angle of the working part from the horizontal; and a controller foradjusting and holding the position of the working part by use of theoperation means based on the angle sensing means.

In one embodiment, the invention may offer the work machine wherein theangle sensing means is installed on the working part.

In one embodiment, the invention may offer the work machine wherein theangle sensing means is installed on the back part of the working part.

In one embodiment, the invention may offer the work machine wherein theangle sensing means is installed on the side part of the working part.

In one embodiment, the invention may offer the work machine furthercomprising: a driver's seat for the operator, a working part controllever installed at the side of the driver's seat, for turning theworking part around by the operator, and an angle control switchequipped on the working part control lever, for starting adjusting andholding the working part to a target angular position.

Advantages of the Invention

The invention offers a work machine having: a working part; a holdingpart for holding the working part; and an operating part for rotatingthe working part around the holding part;

further comprising: an angle sensing means for sensing the angle of theworking part from the horizontal; and a controller for adjusting andholding the position of the working part by use of the operation meansbased on the angle sensing means. Therefore, the bucket can be easilykept level by even an unskilled operator (a driver).

In one embodiment, the invention offers the work machine wherein theangle sensing means is installed on the working part. Therefore, theangle position of the working part can be easily sensed by the anglesensing means.

In one embodiment, the invention offers the work machine wherein theangle sensing means is installed on the back part of the working part.Therefore, the angle position of the working part can be easily sensedby the angle sensing means.

In one embodiment, the invention offers the work machine wherein theangle sensing means is installed on the side part of the working part.Therefore, the angle position of the working part can be easily sensedby the angle sensing means.

In one embodiment, the invention offers the work machine furthercomprising: a driver's seat for the operator, a working part controllever installed at the side of the driver's seat, for turning theworking part around by the operator, and an angle control switchequipped on the working part control lever, for starting adjusting andholding the working part to a target angular position. Therefore, theworking part angle control can be easily operated with the working partcontrol lever while the working part is operated.

BRIEF DESCRIPTION OF THE DRAWINGS

[FIG. 1] A front perspective view of a tractor (a work machine) with afront loader as a first embodiment of the invention.

[FIG. 2] (a) is a back view of the bucket, (b) is a side view from “B”in (a), (c) is a side view of the hitch, and (d) is a section view from“X” in (c).

[FIG. 3] (a) is a front view of the boom control lever and the bucketcontrol lever, (b) is a side view of the bucket control lever from “A”in (a), (c) is a side view of the boom control lever from “A” in (a).

[FIG. 4] A hydraulic circuit in the first embodiment.

[FIG. 5] A block diagram of the main part.

[FIG. 6] A flow chart of the automatic bucket level control process.

[FIG. 7] (a) is a back view of the bucket, (b) is a side view from “C”in (a).

[FIG. 8] A front perspective view of the main features of a tractor (awork machine).

[FIG. 9] (a) is a front view of the boom-bucket control lever, (b) is aplane view of (a), (c) is a right-side view of the boom-bucket controllever, (d) is a front view of the boom-bucket control lever.

[FIG. 10] A hydraulic circuit.

[FIG. 11] A block diagram of the main part.

DETAILED DESCRIPTION OF THE INVENTION Best Mode of Embodying theInvention

The best mode of embodying the invention is described below withreference to specific figures. FIG. 1 shows a front perspective view ofthe tractor 10 (a work machine). The tractor 10 is composed of fronttires 14, rear tires 15 and a front loader 16. In this specification,‘front’ is defined as the direction when the tractor 10 is goingforward, and ‘back’ as the direction when the tractor 10 is goingbackward. Furthermore, ‘left’ is defined as the left side when thetractor 10 is going forward, and ‘right’ is defined as the right sidewhen the tractor 10 is going forward.

A hood 12 is put in the front part of the tractor 10. A tank of gas andan engine (not illustrated) are installed under the hood 12. A frame 41is put in the lower part of the tractor 10, and the engine is mounted onthe frame 41. The power of the engine is transmitted to front tires 14and rear tires 15 through a transmission (not illustrated). The power ofthe engine is also used for a hydraulic pump, which is described below.

A driver's seat 17, on which a driver sits when operating the tractor10, is at the rear part of the tractor 10. A steering wheel 18, amonitor (not illustrated) etc. are in front of the driver's seat 17. Themonitor is to show driving speed, fuel level, etc. and also to give analarm when a tilt sensor (described below) is not working. A bucketcontrol lever (a working part control lever) 19 and a boom control lever20 are installed at the right side of the driver's seat 17. Atransmission (not illustrated) for changing gears of the tractor 10 isunder the driver's seat 17.

A floor 13 is installed in front of the driver's seat 17. The floor 13is composed of a pair of plane parts of the floor 13 a and a projectionpart of the floor 13 b. The two plane parts of the floor 13 a are madeplane and board-like. The projection part of the floor 13 b is installedbetween the two plane parts of the floor 13 a. The projection part ofthe floor 13 b and the two plane parts of the floor 13 a are coupledwith each other by bolts etc. The projection part of the floor 13 bbends upward, and a driving shaft, which transmits power from the engineto the transmission, is located under the projection part of the floor13 b.

Fenders F are mounted on both sides of the driver's seat 17. The bucketcontrol lever 19 and the boom control lever 20 are at the fender F atthe right side of the driver's seat 17. A Rollover Protective Structure(ROPS) R, which is an arch-like safety protective frame, is almostvertically installed at the rear part of the fenders F.

A boom holding mechanism 40 for holding the front loader 16 is installedon both sides and in the middle of the tractor 10.

The front loader 16 is detachable from the tractor 10. The front loader16 is composed of a pair of booms (a support part) 21 set up at bothsides of the tractor 10, a pair of lift cylinders 23 located at bothsides of the main body of the tractor 10, a bucket (working part) 26 anda pair of dump cylinders (operating part) 24. The lift cylinders 23 areto move the boom 21 up and down. The bucket 26 is coupled with the topof the two booms 21. The dump cylinders 24 are to turn the bucket 26around the top of the booms 21. The lift cylinders 23 and the dumpcylinders 24 are connected with a hydraulic circuit. This hydrauliccircuit is to operate the lift cylinders 23 and the dump cylinders 24 byhydraulic pumps, which work by the power from the engine.

The booms 21 are shaped as an arc and stretch out toward the front ofthe tractor 10. The bottom of each of the booms 21 is coupled with theupper section of the boom holding mechanism 40, and the two booms 21(which are located at both sides of the main body of the tractor 10) arerotatable around the boom holding mechanism 40. The bucket 26, on theother hand, is coupled with the two booms 21 by a hitch (a connectionpart) 25. The hitch 25 is detachable from the bucket 26, and isrotatable around the top of the booms 21. A cylinder bracket 27 iswelded at the middle section of each boom 21. The cylinder bracket 27 isset upward from the boom 21 in its front part, whereas it is setdownward from the boom 21 in its rear part.

The bucket 26 is made of metal. It is comprised of a bottom part 26 bt,a pair of side parts 26 s, a rear part 26 bk, a back part 26 b and a toppart 26 u. The side parts 26 s are vertically installed at both ends ofthe bottom part 26 bt. The rear part 26 bk is connected to the pair ofside parts 26 s at both of its ends. The back part 26 b is connected tothe rear part 26 bk, and it is also connected to the pair of side parts26 s at both of its ends. A pair of stays 26A is put on the rear part 26b. A hook bar 26B is fixed to the pair of stays 26A at its both ends. Atilt sensor (an angle sensing means) TS is equipped on the right sidepart 26 s. Alternatively, the tilt sensor TS may be equipped on the leftside part 26 s. The tilt sensor TS senses the angle position of thebucket 26 from the horizontal; in other words, it senses the anglebetween an upper edge 26 su of the side part 26 s and the horizontal.Alternatively, the tilt sensor TS may sense the angle position of thebucket 26 from the vertical. The tilt sensor TS is connected to acontroller (later described).

The hitch 25 is comprised of a pair of trapezoidal metal plates. Eachboom 21 is held at its top between the two metal plates and is rotatableat Pin P. Each dump cylinder 24 is also held at its top between the twometal plates and is rotatable at this point. Pin P is called a rotationcenter of the hitch 25 and the bucket 26. A holding part 25A is made atthe top edge of the hitch 25. The holding part 25A is made by cuttingthe hitch 25 in a half circle shape. The holding part 25A holds a hookpart 26B of the bucket 26. Therefore, the bucket 26 is connected to thehitch 25 via the holding part 25A. A pair of stays 26A is made of arectangular metal plate and is fixed on the rear part 26 bk of thebucket 26.

Other attachments instead of the bucket 26 can also be attached to thehitch 25. A harness, which connects between the tilt sensor TS and theabove-mentioned controller, has a connecter. The harness can bedisconnected from the bucket 26 at said connecter when the bucket 26 isdetached. When another attachment is attached to the hitch 25, theharness is to be connected to the attachment with the connecter. A swingsensor or a gyro sensor can be installed in the bucket 26 instead of thetilt sensor TS.

The bottom of the lift cylinder 23 is coupled with the boom holdingmechanism 40 and is rotatable at the boom holding mechanism 40. The topof the lift cylinder 23 is, on the other hand, connected to the backpart of the cylinder bracket 27 and is rotatable at the cylinder bracket27. Each lift cylinder 23 is installed underneath and parallel to eachboom 21.

The dump cylinder 24 is connected to the front part of the cylinderbracket 27 and is rotatable at the cylinder bracket 27. On the otherhand, the top of the dump cylinder 24 is coupled with the top of thehitch 25 and is rotatable at the hitch 25. Each dump cylinder 24 isinstalled over each boom 21.

Therefore, the booms 21 go up (or rotate upward) when the lift cylinders23 stretch out, whereas the booms 21 go down (or rotate downward) whenthe lift cylinders 23 shrink. On the other hand, the bucket 26 turnsupward when the dump cylinders 24 shrink, whereas the bucket 26 turnsdownward when the dump cylinders 24 stretch out.

The bucket control lever 18 and the boom control lever 20 areillustrated in FIG. 3( a) to FIG. 3( c), and the hydraulic circuit isillustrated in FIG. 4. The bucket control lever 19 is to operate thedump cylinders 24 of the front loader 16. The bucket control lever 19consists of a grip 19 a, a rod 19 b and a protection part 19 c. The grip19 a is made of resin and shaped by an injection molder. The lower partof the rod 19 b is held inside the right fender F. The protection part19 c covers the gap between the rod 19 b and the fender F in order toprevent dust from coming inside the fender F. The protection part 19 cis made of a flexible material to enable it to follow the movement ofthe rod 19 b. The bucket control lever 19 is connected to a selectorvalve 50. The selector valve 50 changes position when the bucket controllever 19 is turned.

More specifically, when the bucket control lever 19 is turned toward theD direction, the selector valve 50 moves to the D position (DOWNposition). When the bucket control lever 19 is turned toward the Udirection, the selector valve 50 moves to the U position (UP position).The bucket control lever 19 is always in the N position (neutral) bycoil springs (not illustrated) whenever it is not operated. Operationbuttons B1, B2 are installed on the front side of the bucket controllever 19. Furthermore, operation buttons B1, B2 project from the frontside of the bucket control lever 19. An operation button B3 is installedon the upper side of the bucket control lever 19. Furthermore, theoperation button B3 projects from the upper side of the bucket controllever 19. Each operation button B1, B2, B3 is made of resin and is acolumn with a dome-like tip. The back of the operation buttons B1, B2,B3 are flat. The actuator of each switch (the switch is a push-plungertype limit switch with the actuator) touches the back of the operationbuttons B1, B2 and B3, respectively.

Three switches of the operation buttons B1, B2, B3 are respectivelyconnected to the controller (described later). The solenoid valve SL ismoved to the position U when the operation button B1 is pressed. On theother hand, the solenoid valve SL is moved to the position D when theoperation button B2 is pressed. The automatic bucket level control forthe bucket 26 starts when the operation button (an angle control switch)B3 is pressed (and then the switch is ON). The automatic bucket levelcontrol for the bucket 26 ends when the operation button (an anglecontrol switch) B3 is pressed again (and then the switch is OFF).

The boom control lever 20 is to operate the lift cylinders 23. The boomcontrol lever 20 consists of a grip 20 a, a rod 20 b and a protectionpart 20 c. The grip 20 a is made of resin and shaped by an injectionmolder. The lower part of the rod 20 b is held inside the right fenderF. The protection part 20 c covers the gap between the rod 20 b and thefender F in order to prevent dust from entering the fender F. Theprotection part 20 c is made of a flexible material to enable it tofollow the movement of the rod 20 b. The boom control lever 20 isconnected to a selector valve 51. The selector valve 51 changes positionwhen the boom control lever 20 is turned.

More specifically, when the boom control lever 20 is turned toward the Ddirection, the selector valve 51 moves to the D position (DOWNposition). When the boom control lever 20 is turned toward the Udirection, the selector valve 51 moves to the U position (UP position).The boom control lever 20 is always in the N position (neutral) by coilsprings (not illustrated) whenever it is not operated.

The hydraulic circuit is connected to the hydraulic fluid tank (notillustrated). The hydraulic fluid can move with a constant pressurebetween the hydraulic fluid tank and the dump cylinders 24 when thebucket control lever 19 is in operation. The hydraulic fluid can movewith a constant pressure between the hydraulic fluid tank and the boomcylinders 23 when the boom control lever 20 is in operation. The dumpcylinders 24 expand when the bucket control lever 19 is turned towardthe D direction. On the other hand, the dump cylinders 24 shrink whenthe bucket control lever 19 is turned toward the U direction. The liftcylinders 23 shrink when the boom control lever 20 is turned toward theD direction. On the other hand, the lift cylinders 23 expand when theboom control lever 20 is turned toward the U direction.

The procedure for operating the front loader 16 by use of the bucketcontrol lever 19 and the boom control lever 20 is described as follows:In order to move the booms 21 upward, turn the boom control lever 20toward the operator's side (the U direction). The selector valve 51moves toward the U position. Then, the hydraulic circuit of the liftcylinders 23 is opened to expand the lift cylinders 23. In order to stopmoving the booms 21 upward, release your hand from the boom controllever 20. The boom control lever 20 returns to the N position and theselector valve 51 moves toward the N position to close the hydrauliccircuit of the lift cylinders 23.

In order to move the booms 21 downward, turn the boom control lever 20frontward (the D direction). The selector valve 51 moves toward the Ddirection. Then, the hydraulic circuit of the lift cylinders 23 isopened to shrink the lift cylinders 23. In order to stop moving thebooms 21 downward, release your hand from the boom control lever 20. Theboom control lever 20 returns to the N position, and the selector valve51 moves toward the N position for closing the hydraulic circuit of thelift cylinders 23.

In order to move the bucket 26 upward, turn the bucket control lever 19backward (the U direction). The selector valve 50 moves toward the Udirection. Then, the hydraulic circuit of the dump cylinders 24 isopened to shrink the dump cylinders 24. In order to stop moving thebucket 26 upward, release your hand from the bucket control lever 19.The bucket control lever 19 returns to the N position, and the selectorvalve 50 moves toward the N position for closing the hydraulic circuitof the dump cylinders 24.

In order to move the bucket 26 downward, turn the bucket control lever19 frontward (the D direction). The selector valve 50 moves toward the Ddirection. Then, the hydraulic circuit of the dump cylinders 24 isopened to expand the dump cylinders 24. In order to stop moving thebucket 26 downward, release your hand from the bucket control lever 19.The bucket control lever 19 returns to the N position and the selectorvalve 50 moves toward the N position to close the hydraulic circuit ofthe dump cylinders 24.

The bucket 26 can also be operated upwardly or downwardly by theoperation buttons B1 and B2, respectively. The solenoid valve SL movestoward the U position when the operation button B1 is pressed while thebucket control lever 19 is in the N position. The solenoid valve SLmoves back to the N position when your hand is released from theoperation button B1. The solenoid valve SL moves toward the D positionwhen the operation button B2 is pressed while the bucket control lever19 is in the N position. The solenoid valve SL moves back to the Nposition when your hand is released from the operation button B2. Thecontroller (described later) is in between the operation buttons B1, B2and the solenoid valve SL. The solenoid valve SL is moved by thecontroller.

FIG. 5 shows the main block diagram of this embodiment (the engine isdescribed as “E”). The controller (a control part) CT, which is inside adashboard in front of the driver's seat 17, is connected with theoperation buttons B1, B2, B3. The controller CT is also connected withthe tilt sensor TS. Furthermore, the controller CT is connected to thesolenoid valve SL and operates it.

The controller CT is able to conduct the automatic bucket level controlprocess for the bucket 26, which keeps the bucket 26 level. FIG. 6 showsthe automatic bucket level control program flow chart for the controllerCT. The controller CT periodically senses if the tilt sensor TS isworking (STEP1). If the tilt sensor TS is not working, the controller CTgives an alarm on the display, which is installed in front of thedriver's seat 17 (STEP2). If the tilt sensor TS is working, thecontroller CT program proceeds to STEP3 and the controller CT senses ifthe operation button (the automatic level control button) B3 is ON. Ifthe operation button B3 is OFF, then, the controller CT program proceedsto STEP4 and the controller CT ends the automatic level control program(or the controller CT does not start the program). If the operationbutton B3 is ON, then the controller CT program proceeds to STEP5 andthe controller CT starts the automatic level control program.

Furthermore, at STEP6, the controller CT periodically senses if thebucket 26 is level via the tilt sensor (an angle sensing means) TS. Ifthe bucket 26 is level, the controller CT program goes back to STEP3. Ifthe bucket 26 is not level, the controller CT program goes to STEP7 andthe controller CT senses if the upper edge 26 su of the bucket 26 isturning more than the level (the horizontal) or, in other words, theupper edge 26 su is turning backward (toward the driver' seat 17) morethan the level. If the upper edge 26 su is turning more than the level,the controller CT moves the solenoid valve SL toward the DOWN positionto expand the dump cylinder 24 (STEPS). If the upper edge 26 su is notturning more than the level, the controller CT program proceeds to STEPSand the controller CT senses if the upper edge 26 su is turning lessthan the level. If the upper edge 26 su is not turning less than thelevel, the controller CT program goes back to STEP1. If the upper edge26 su is turning less than the level (the horizontal), the controller CTmoves the solenoid valve SL toward the UP position for shrinking thedump cylinder 24 (STEP10).

The automatic level control precedes the bucket manual operation withthe operation buttons B1, B2.

The automatic level control program in this embodiment can be appliednot only to the horizontal control of the bucket but also angle controlof the bucket in any plane—it is called an automatic angle controlprogram. In such cases, an angle set dial, which is connected to theoperation button B3, should be set on the bucket control lever 19 inorder to automatically control the bucket angle with respect to thelevel. In addition, the target angle of the bucket 26 may be inputthrough a touch screen display.

Further Embodiment 1

FIG. 7 shows a further embodiment of this invention. In this embodiment,a tilt sensor TS1 is installed on the rear part 26 bk of the bucket 26.Other components of the tractor 10 are not described as they are thesame as the previous embodiment.

The bucket 26 is made of metal. It is comprised of a bottom part 26 bt,a pair of side parts 26 s, a rear part 26 bk, a back part 26 b and a toppart 26 u. The side parts 26 s are vertically installed at both ends ofthe bottom part 26 bt. The rear part 26 bk is connected to the sideparts 26 s at both of its ends. The back part 26 b is connected to therear part 26 bk and is also connected to the pair of side parts 26 s atboth of its ends. A pair of stays 26A is put on the rear part 26 b. Ahook bar 26B is fixed to the pair of stays 26A at both of its ends. Atilt sensor (an angle detection means) TS1 is equipped underneath thehook bar 26B. Alternatively, the tilt sensor TS1 may be equipped on thetop part 26 u or the back part. The tilt sensor TS1 is to sense theangle position of the bucket 26 from the horizontal; however, the tiltsensor TS1 may sense the angular position of the bucket 26 from thevertical, instead. The tilt sensor TS1 is connected to a controller CTwith a harness.

The automatic bucket level control process, which gives an automaticlevel control for the bucket 26, is the same as the previous embodimentshown in FIG. 6. If the tilt sensor is installed on the side part 26 s,as described in the previous embodiment, the tilt sensor might be brokenby sand or rocks when the tractor 10 digs. However, if the tilt sensorTS1 is installed on the rear part 26 bk (or the upper part 26 u, theback part 26 b), the risk of the tilt sensor TS1 being brokenunexpectedly as just described can be reduced.

Further Embodiment 2

Another embodiment of this invention is shown in FIG. 8 to FIG. 11. Inthis embodiment, a boom-bucket control lever JS is introduced instead ofthe bucket control lever 19 and the boom control lever 20. In thisembodiment, the boom-bucket control lever JS has two functions: a bucketcontrol function and a boom control function. The boom-bucket controllever JS is positioned on the fender F. Other components of the tractor10 are the same as the first embodiment. When the boom-bucket controllever JS is turned frontward or backward (BD-BU direction in FIG. 9),the selector valve 51 is operated and the booms 21 are turned. On theother hand, when the boom-bucket control lever JS is turnedleft-sideward or right-sideward (AU-AD direction in FIG. 9), theselector valve 50 is operated and the bucket 26 is turned. Operationbuttons B1, B2 are installed on the front side of the boom-bucketcontrol lever JS. Furthermore, operation buttons B1, B2 project from thefront side of the boom-bucket control lever JS. An operation button B3is installed on the upper side of the boom-bucket control lever JS.Furthermore, the operation button B3 projects from the upper side of theboom-bucket control lever JS.

The hydraulic circuit is connected to the hydraulic fluid tank (notillustrated). The hydraulic fluid can move with a constant pressurebetween the hydraulic fluid tank and the dump cylinders 24 when theboom-bucket control lever JS is in operation. The hydraulic fluid canmove with a constant pressure between the hydraulic fluid tank and theboom cylinders 23 when the boom-bucket control lever JS is in operation.The dump cylinders 24 expand when the boom-bucket control lever JS isturned toward the AD direction. On the other hand, the dump cylinders 24shrink when the boom-bucket control lever JS is turned toward the AUdirection. The lift cylinders 23 shrink when the boom-bucket controllever JS is turned toward the BD direction. On the other hand, the liftcylinders 23 expand when the boom-bucket control lever JS is turnedtoward the BU direction.

The procedure for operating the front loader 16 by use of theboom-bucket control lever JS is described as follows: in order to movethe booms 21 upward, turn the boom-bucket control lever JS backward (theBU direction). The selector valve 51 moves toward the BU position. Then,the hydraulic circuit of the lift cylinders 23 is opened to expand thelift cylinders 23. In order to stop moving the booms 21 upward, releaseyour hand from the boom-bucket control lever JS. The boom-bucket controllever JS returns to the N position and the selector valve 51 movestoward the N position to close the hydraulic circuit of the liftcylinders 23.

In order to move the booms 21 downward, turn the boom-bucket controllever JS forward (the BD direction). The selector valve 51 moves towardthe BD direction. Then, the hydraulic circuit of the lift cylinders 23is opened to shrink the lift cylinders 23. In order to stop moving thebooms 21 downward, release your hand from the boom-bucket control leverJS. The boom-bucket control lever JS returns to the N position, and theselector valve 51 moves toward the N position for closing the hydrauliccircuit of the lift cylinders 23.

In order to move the bucket 26 upward, turn the boom-bucket controllever JS left-sideward (the AU direction). The selector valve 50 movestoward the AU direction. Then, the hydraulic circuit of the dumpcylinders 24 is opened to shrink the dump cylinders 24. In order to stopmoving the bucket 26 upward, release your hand from the boom-bucketcontrol lever JS. The boom-bucket control lever JS returns to the Nposition, and the selector valve 50 moves toward the N position forclosing the hydraulic circuit of the dump cylinders 24.

In order to move the bucket 26 downward, turn the boom-bucket controllever JS right-sideward (the AD direction). The selector valve 50 movestoward the AD direction. Then, the hydraulic circuit of the dumpcylinders 24 is opened to expand the dump cylinders 24. In order to stopmoving the bucket 26 downward, release your hand from the boom-bucketcontrol lever JS. The boom-bucket control lever JS returns to the Nposition and the selector valve 50 moves toward the N position to closethe hydraulic circuit of the dump cylinders 24.

As with the previous embodiments, the bucket 26 can also be operatedupwardly or downwardly by the operation buttons B1 and B2, respectively.The solenoid valve SL moves toward the U position when the operationbutton B1 is pressed while the boom-bucket control lever JS is in the Nposition. The solenoid valve SL moves back to the N position when yourhand is released from the operation button B1. The solenoid valve SLmoves toward the D position when the operation button B2 is pressedwhile the boom-bucket control lever JS is in the N position. Thesolenoid valve SL moves back to the N position when your hand isreleased from the operation button B2. The controller CT is in betweenthe operation buttons B1, B2 and the solenoid valve SL. The solenoidvalve SL is moved by the controller CT. The automatic bucket levelcontrol program flow chart shown in FIG. 6 applies to this embodiment.

1. A work machine having: a working part; a holding part for holding theworking part; and an operating part for rotating the working part aroundthe holding part; further comprising: an angle sensing means for sensingthe angle of the working part from the horizontal; and a controller foradjusting and holding the position of the working part by use of theoperation means based on the angle sensing means.
 2. The work machine asset forth in claim 1 wherein the angle sensing means is installed on theworking part.
 3. The work machine as set forth in claim 1 wherein theangle sensing means is installed on the back part of the working part.4. The work machine as set forth in claim 1 wherein the angle sensingmeans is installed on the side part of the working part.
 5. The workmachine as set forth in claim 1, further comprising: a driver's seat forthe operator, a working part control lever installed at the side of thedriver's seat, for turning the working part around by the operator, andan angle control switch equipped on the working part control lever, forstarting adjusting and holding the working part to a target angularposition.